Japanese Laid-Open Patent Publication No. 2005-298163 describes a prior art example of a cargo handling controller for a cargo handling vehicle. The cargo handling vehicle includes an engine, a generator-motor, and a cargo handling pump, which are arranged so as to be coaxial to one another. The cargo handling vehicle switches the operation modes of the generator-motor between generator mode and motor mode. More specifically, when a cargo handling operation does not require a high output, the generator-motor is switched to the generator mode, and the pump is driven by the engine. When a cargo handling operation requires a high output, the generator-motor is switched to the motor mode, and the generator-motor assists the engine in driving the pump.
Japanese Laid-Open Patent Publication No. 2001-173024 discloses a construction machine including an engine, a rotary electrical device (generator-motor), and a hydraulic pump, which are arranged so as to be coaxial to one another. The rotary electrical device is operated as a generator and a motor. More specifically, the rotary electrical device is operated as a generator when an operational angle of an operation lever is less than or equal to a predetermined angle. The rotary electrical device is operated as a motor when the operational angle of the operation lever is greater than the predetermined angle. A drive command is output so as to control the output of the rotary electrical device in accordance with the operational angle of the operation lever. Further, when there is a decrease in the speed of the rotation produced by the engine (engine rotation speed), the construction machine operates the rotary electrical device as a motor and feedback controls the rotary electrical device based on the engine rotation speed.
In the construction machine, the output of the rotary electrical device is controlled based on the comparison of a target engine rotation speed and an actual engine rotation speed. However, in an electric power generation system (engine to generator-motor), there is normally a long delay until the actual rotation responds to a drive command. Thus, the present actual engine rotation speed would be the result of a response to a target engine rotation speed that was given a predetermined time earlier. Accordingly, in a feedback control system that compares the present target engine rotation speed and the present actual engine rotation speed, response delays may result in excessive or insufficient corrections. This may cause the cargo handling assistance amount of the generator-motor to be excessive or insufficient and consequently lower the cargo handling capacity.